This application claims priority to an application entitled Device And Method For Forming Optical Fiber Gratings By Microbending filed in the Korean Industrial Property Office on Mar. 11, 1999 and assigned Serial No. 99-8081, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a device and method for forming optical fiber gratings by microbending, and in particular, to a device and method for forming optical fiber gratings by subjecting an optical fiber to microbending using CO2 laser beams.
2. Description of the Related Art
Long-period fiber gratings (LPFGs) are widely used in applications of a wavelength filter with a low reflectance, a gain flattening filter of an erbium-doped fiber amplifier (EDFA), and an optical fiber sensor.
In prior art, LPFGs are formed by changing the refractive index of an optical fiber core using photosensitiveness or residual stresses, or transforming the core by partial removal of a cladding. The photosensitiveness using method, however, cannot be applied to an optical fiber non-photosensitive and requires hydrogen treatment to increase photosensitiveness. Formation of LPFGs by relieving residual stresses does not produce a high filtering effect on an optical fiber in which many mechanical stresses do not remain. Furthermore, the transformation of the core by partial removal of the cladding remarkably decreases the tensile strength of an optical fiber.
Incorporated herein by reference are: U.S. Pat. No. 5,715,263 to Brian F. Ventrudo et al. entitled Fibre-Grating-Stabilized Diode Laser teaches the use of a fibre Bragg grating to stabilize the intensity and frequency fluctuations of a diode laser; U.S. Pat. No. 5,384,884 to Raman Kashyap et al. entitled Method Of Forming Optical Fibre Gratings teaches applying different longitudinal stresses to a fiber each time a Bragg grating is written with an Argon ion laser; EP Patent No. 0884612 to Michael G. Wickham entitled Method Of And Apparatus For The Automated Precision Wavelength Control Of Fiber Optic Bragg Grating Writing provides a computer controlled apparatus using a laser to generate a UV beam and a rotatable prism to write Bragg gratings on an optical fiber; U.S. Pat. No. 6,011,886 to Anatoli A. Abramov et al. entitled Recoatable Temperature Insensitive Long-Period Gratings which discuses the use of fiber""s having long-period gratings; U.S. Pat. No. 5,555,086 to Karlheinz vonBieren et al. entitled Coherence Multiplexed Interferometric Signal Processing System And method describes the formation of microbends in a length of optical fiber to form a modal coupler; U.S. Pat. No. 5,216,739 to Kenneth O. Hill et al. entitled Method Of Creating An index Grating in An optical Fiber and A Mode Converter Using The Index Grating discusses exposing the fiber to UV light beams to obtain fiber gratings; U.S. Pat. No. 5,708,740 to Thomas John Cullen entitled Optical Notch Filter manufacture In Optical Fibre Waveguide By Plastic Deformation describes a technique of using a micro-flame to form microbends in a stretched optical fiber to create a notch filter; U.S. Pat. No. 5,796,906 to Chellappan Narayanan et al. entitled optical Planar Waveguide Notch Filters provides a background discussion regarding the differences between core deformed fibers and long-period grating in notch filters and provides an alternative notch filter which utilizes symmetrical corrugations formed using either a heater or a CO2 laser; U.S. Pat. No. 5,411,566 to Craig. D. Poole et al. entitled Optical Fiber Spatial Mode Converter Using Periodic Core Deformation describes the use of a laser to abulate material from the side of a fiber at periodic intervals along its length and then heating those regions so that resulting surface tension effects deform the core sinusoidally; and U.S. Pat. No. 6,003,340 to Georges Borak et al. entitled Method Qf Putting A Bend into A Fiber To Make A Strain Sensor describes using a CO2 laser as a heating source to form an S-shaped microbend.
It is, therefore, an object of the present invention to provide a device and method for forming fiber gratings by microbending using a CO2 laser beam.
The above object can be achieved by providing an optical fiber grating forming device and method. In the optical fiber grating forming device, a laser system emits a CO2 laser beam, a lens focuses the CO2 laser beam on an optical fiber in a predetermined width, an optical fiber support fixes both ends of the optical fiber and imparts tensile strain to the optical fiber, and a controller controls the intensity of the CO2 laser beam, the focusing distance of the lens, and the tensile force applied by the optical fiber support.
According to another aspect of the prevent invention, the optical fiber grating forming method includes the steps of focusing a CO2 laser beam on an optical fiber with a predetermined width, fixing both ends of the optical fiber and applying tensile force to the fixed optical fiber, projecting the CO2 laser beam onto a predetermined portion of the optical fiber to which tensile force is applied, repeating the above steps, while moving the optical fiber at predetermined intervals.